The disclosure relates generally to superconducting systems and more specifically to systems and methods for alternatingly switching a persistent current switch between a resistive mode and a superconductive mode in magnetic resonance imaging (MRI) systems.
A superconducting magnet is used to produce a magnetic field in MRI systems. In some methods, an electric current from a power source is constantly applied to the superconducting magnet to produce the magnetic field. However, production of such a strong magnetic field entails a constant supply of the electric current in a range of hundreds of amperes. This constant supply of electric current to the superconducting magnet increases the running cost of the MRI system.
Furthermore, in certain other techniques, the superconducting magnet is excited to operate in a persistent current mode, where the electric current persistently flows in a superconducting loop without any current supply from the power source. Particularly, a persistent current switch is coupled in parallel to the superconducting magnet and the power source. Moreover, the persistent current switch is alternatingly switched from a normal state to a superconducting state to operate the superconducting magnet in the persistent current mode. These techniques are widely used in magnetic devices, such as MRI systems. However, while operating in the normal state, enormous amount of heat is produced by the persistent current switch. It is desirable to optimally dissipate this heat from the persistent current switch to transition the switch from the normal state to the superconducting state without high boil-off of cryogen in the MRI system.
In a conventional system, a superconducting magnet is housed in a helium vessel containing about 2000 liters of liquid helium (He). Further, the persistent current switch is fitted around the superconducting magnet with the persistent current switch immersed in this helium vessel. Since this arrangement employs a large vessel with thousands of liters of liquid He, the arrangement is not only expensive to manufacture, but also heavy to transport and install at a desired location, e.g., diagnostic centers. Additionally, the refill of thousands of liters of liquid He for delivery to remote locations after completing the ride through to the customer, may be inconvenient.
Moreover, the liquid He in these systems can sometimes boil-off during a quench event. The boiled-off helium escapes from the cryogen bath in which the magnetic coils are immersed. Thus, each quench event is followed by re-filling of the liquid He and re-ramping of the magnet, which is an expensive and time consuming event. Additionally, in conventional magnetic devices, a sophisticated exterior venting system is needed to vent the gas, such as boiled-off helium, through venting pipe stacks after the magnet and/or the switch quenches. However, the venting pipes are difficult to install. Also, in some situations, the venting of helium can have environmental or regulatory concerns. Thus, conventional MRI magnet designs and their cooling arrangements can entail special installation requirements, the inability to install these systems in certain regions, and a high maintenance cost.